A head suspension assembly is an apparatus in a hard disk drive that positions a read/write head assembly over the spinning surface of a data storage device (e.g. a magnetic hard disk). The head suspension assembly is one of the smallest and most delicate components of a disk drive. The head suspension assembly includes a suspension assembly and a head assembly, with the head assembly positioned at a distal end of the suspension assembly. The suspension assembly is an elongated structure having a spring region or element therein. Suspension assemblies act in a similar fashion to the needle arm in a record player, positioning the head assembly generally less than fifteen nanometers from a surface of a spinning disk in the disk drive. The suspension assembly is attached to an actuator arm, which rotatably positions the suspension assembly and head assembly into the proper position for reading from or writing to the magnetic disk.
Suspension assemblies generally include component elements such as an elongated load beam, a flexure, and a base plate or other mounting means. The load beam is attached to the base plate or other mounting means at a mounting region of the load beam, located at a proximal end of the load beam. Extending from the mounting region of the load beam is a spring region (also known as a “radius region”), which permits some degree of bending in the assembly. The flexure is attached to the load beam at least at a distal end of the load beam. Between the spring region and the flexure is a relatively rigid region of the load beam. In some configurations, a stiffener is attached to the load beam or other component to provide added rigidity or to provide a preload force to the head assembly; see, for instance, U.S. Pat. No. 5,793,569 to Christianson, et al.
The read/write head assembly is mounted to the flexure. The flexure provides gimballing support to the head assembly, so that the head assembly can closely track the contours of the surface of the spinning disk. The head assembly includes an air bearing slider and a read/write magnetic transducer formed on the slider. The slider is a head assembly element aerodynamically shaped to use the air stream generated by the spinning disk to produce a lift force which supports the head assembly above the disk.
During operation of the disk drive, the whole suspension assembly is designed to work together to maintain the head assembly at a desired orientation with respect to the surface of the spinning disk. A design goal for magnetic disk drives is to “fly” the head at the closest possible distance and at a desired attitude with respect to the surface of the disk. As the disk spins beneath the head, an air bearing is formed between the disk and the slider as air is forced under the slider. The air bearing prevents the head assembly from “crashing” into the surface of the disk. Simultaneously, a compensating force is required to prevent the air bearing from forcing the head assembly too far away from the surface of the disk. The spring region of the load beam, which is usually made from stainless steel sheets 25 to 100 μm thick, generally provides a force known as a gram load to compensate for the lift that results from the air bearing.
As the head assembly hovers above the magnetic hard disk, electric signals must be coupled to the read/write head. Early technology used wires that ran from the head to the controlling electronics. Modern head suspension assemblies utilize integral conductive leads, or “traces,” that allow communication with the read/write head and eliminate the need for discrete wires; see, for example, U.S. Pat. Nos. 5,812,344 and 5,737,152 to Balakrishnan and U.S. Pat. No. 5,754,368 to Shiraishi, et al. A suspension component possessing integral leads can be referred to as an integrated lead suspension component. For example, a flexure incorporating integrated traces can be called an integrated lead flexure.
Welds are often used for attachment of two or more suspension components during manufacture of the suspension assembly. By way of example, the load beam and the flexure may be attached together by welds. During welding, intense heat is applied to weld points on the surface of the elements to be welded. A zone of molten material is created, permitting material from the elements to flow and bond. The molten zone is then allowed to cool. Since the zone loses heat to the outside atmosphere and to the surrounding material, the zone cools from the outside in, contracting and solidifying as it cools. Once the zone has cooled, the solidified material holds the suspension assembly elements together.
Welds for attaching components can be formed by, for example, laser-welding or spot-welding techniques. Laser welding is performed using a laser beam, which locally heats a material by irradiation. See, for instance, U.S. Pat. No. 5,201,458 to Hagen, which discusses the dynamics of the formation of a laser weld. Spot welding is done by discharging a high electrical current through the material to be welded using electrodes positioned on opposing surfaces of the materials to be welded. Resistive heating of the material melts the material and creates the weld. See, for instance, U.S. Pat. No. 4,755,652 to La Rocca.
Although welding is the most common means of attaching head suspension components together to make head suspension assemblies, problems have been observed with the use of welds. One major drawback is that such welds can leave residual stresses in the component structures, due to the contraction of the component material during cooling. Residual stresses have been found to affect static attitude of the head suspension assembly. Efforts to reduce residual stresses have included the use of holes in the components near the welds, preheating of the weld area prior to welding, or application of pressure after welding; see U.S. Pat. No. 5,748,409 to Girard, et al. and U.S. Pat. No. 5,201,458 to Hagen.
A further problem associated with welding that has been identified is a “flapping” phenomenon that results when a weld is located on an interior region of a surface to be attached. When a weld is used near the center of the contact area between components, a gap may form between the surfaces of the attached components. As the disk rotates and creates an air current that impinges upon the suspension assembly, air can be forced into the gap. A vibration, or “flapping,” may result because of the gap between the components. See U.S. Pat. No. 4,786,999 to Tanaka, et al., which attempts to remedy the problem by strategically distributing a plurality of welds.